Debugging material math nodes in cycles
You should activate the plugin "Node Wrangler" (it's awesome). Beside offering many Shortcuts and hotskeys it also offers to view every? possible output. To enable it open File &gt; User Preferences...Ctrl+Alt+U and go to the Addons section. Search for "Node Wrangler":



Next you can go into your node editor and Ctrl+Shift+Left Mouse-click on the output node of your choice. It should have created a Viewer-node that is linked between the selected node and the Material Output.



You can now view the output from the node in any 3d-Viewport after switching to Viewport-Shading Rendered. To render faster you can switch to Object-Local-view. Just select the object you want to view and press Numpad /. This will temporarily disable all other objects and speed up the preview rendering. (If you don't have a Numpad, the setting can be found under View &gt; View Global/Local)



Note: This plugin also offers much functionality. Just press Ctrl+Space in the Node Editor to see it for yourself.